1. Field of the Invention
The present invention relates to a shift range changeover mechanism mounted in a vehicle or the like, more specifically, it relates to a range changeover mechanism with a drive such as an electric motor which operates in response to the operation of shift range selector such as a shift lever, and controls, for example, a hydraulic control device to change a shift range.
2. Related Art
Conventionally, a range changeover mechanism includes a manual valve that changes the shift range within a transmission and a shift lever provided in the interior of a vehicle and connected to the manual valve via a shift cable. Thus, in such a mechanism, the shift lever operates the manual valve via the shift cable with operation by a driver.
However, increased flexibility in location of the shift lever is needed to respond to demands for increasing the degree of freedom in vehicle interior design and for expanding derivative vehicle types from identical platforms. However, the above-mentioned shift cable, which connects the shift lever and the manual valve, has many layout restrictions and the development of a range changeover mechanism that does not use such a shift cable is desired.
Japanese Patent Laid-Open Publication (“Kokai”) No. 7-16067 discloses a range changeover mechanism that changes the shift range using an electric motor (and magnetic clutch) in a so-called shift-by-wire system. In the range changeover mechanism disclosed in this publication, the driving force of an electric motor, responsive to the operation of a shift lever, is transferred to a range control shaft via a predetermined reducer to rotate the control shaft, and the shift range is changed through, for example, operation of a hydraulic control unit of an automatic transmission and a parking mechanism via the detent lever fixed to the control shaft. The above-mentioned demand for greater flexibility regarding the location of installation of the shift lever is answered by such a structure.
In the range changeover apparatus disclosed in Kokai No. 7-16067, by engaging the range control shaft with a sector gear interlocked with and connected to the transmission side downstream of the reducer, the rotation of the sector gear is transferred to the range control shaft. By detecting the rotational position of the detent lever, i.e. the rotational position of the range control shaft, with a position detecting sensor, the current state of range changeover is continuously detected, thereby changing and controlling the shift range.
Known position detecting sensors include, for example, sensors such as an electromagnetic pickup system, a magnetic system using a magnetoresistance element (MRE) and a Hall element, and an optical system using a slit disc and a photo interrupter. All are equipped with a rotor interlocked with and connected to the sector gear or the like, and a sensor body fixed to the casing side of the range changeover mechanism. When using such a position detecting sensor, the rotor and sector gear are splined together to form an integrally rotating structure.
However, in the above-described range changeover mechanism, detection of the precise rotational position of the range control shaft, i.e. the precise rotational position of the detent lever, with a high level of accuracy, becomes difficult due to spline looseness (“play”) between the sector gear and the rotor. Therefore, realization of a range changeover mechanism having a structure that enables execution of shift range control with greater accuracy by precisely detecting the rotational position of the range control shaft is needed.